Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS6160515 A
Publication typeGrant
Application numberUS 09/323,644
Publication dateDec 12, 2000
Filing dateJun 1, 1999
Priority dateJun 1, 1999
Fee statusLapsed
Also published asUS6445348
Publication number09323644, 323644, US 6160515 A, US 6160515A, US-A-6160515, US6160515 A, US6160515A
InventorsDanny O. McCoy, Feng Niu
Original AssigneeMotorola, Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Dispersive surface antenna
US 6160515 A
Abstract
Dispersive surface antenna structures (300, 700) provide improved selectivity and increased control over bandwidth. Antenna structures (300, 700) include a wraparound piece of conductive material located perpendicular to around plane (304, 704). Ground posts (302, 702) extend up from the ground base (304) and capacitively couple to a front conductive surface (301, 701) of the antennas (300, 700). First and second conductive back surfaces (305, 306), (705, 706) are capacitively coupled across a gap (307, 707) along the back of the antennas (300, 700). The size, width, and location of the gap (307, 707) along with the ground posts (302, 702) provide increased control over antenna performance.
Images(7)
Previous page
Next page
Claims(8)
What is claimed is:
1. A dispersive surface antenna, comprising:
a substrate;
a front conductive surface coupled to the substrate;
a radio frequency (RF) feed coupled to the front conductive surface;
first and second conductive back surfaces coupled to the conductive front surface, and separated by a gap, the first and second conductive back surfaces capacitively coupled across the gap;
a conductive ground base; and
at least one ground post coupled between the conductive ground base and the substrate, the at least one ground post capacitively coupled to the front conductive surface.
2. The antenna structure of claim 1, wherein the front conductive surface includes at least one slot for accommodating the at least one ground post.
3. The antenna of claim 1, wherein the at least one ground post provides both physical support and electrical ground for the dispersive surface antenna.
4. The antenna structure of claim 1, wherein the at least one ground post is adjustable to control antenna bandwidth.
5. The antenna structure of claim 1, wherein the gap is located off-center with respect to the front conductive surface to provide multiband performance.
6. The antenna of claim 1, wherein the gap is characterized by an adjustable width.
7. The antenna of claim 1, wherein the antenna is used in a laptop communication device.
8. An antenna assembly, comprising:
first and second dispersive surface antennas,
the first dispersive surface antenna, comprising:
a front conductive surface having a radio frequency (RF) feed;
a conductive post capacitively coupled to the front conductive surface;
first and second conductive back surfaces coupled to the front conductive surface and separated by a gap;
the second dispersive surface antenna, comprising:
a second front conductive surface having an RF feed;
a conductive post capacitively coupled to the second front conductive surface;
third and fourth conductive back surfaces coupled to the second conductive front surface and separated by a gap; and
a balun coupled between the first and second dispersive surface antennas, the balun including first and second shielded portions, the first shielded portion for carrying a radio frequency (RF) signal to the RF feed of the first dispersive antenna, the first shielded portion also being coupled to the conductive post of the second dispersive surface antenna, the second shielded portion being coupled to the second front conductive surface of the second dispersive antenna, the second shielded portion also being coupled to the conductive post of the first dispersive surface antenna, the antenna assembly providing a 180 degree phase shift between the first and second dispersive surface antennas.
Description
TECHNICAL FIELD

This invention relates in general to antennas and more specifically to dispersive surface antennas.

BACKGROUND

The current trend in the wireless communications industry is towards providing multiple services and worldwide coverage. Due to the co-existing multiple standards and the fact that different services are provided on different frequencies, there is an ever-growing need for multi-band operations and thus the need for multi-band antennas. The rapid development of various radio technologies has dramatically reduced radio volume and thickness. Furthermore, there are emerging technologies, such as time domain radios, which require extremely wide bandwidths, usually well over several hundred megahertz (MHz).

When a radio is operated in either dispatch mode (two-way radio) or phone mode (cellular phones, etc.), antenna efficiency is a major concern. High surface current density antennas, such as wire antennas, restrict currents to small areas. This creates larger near field power densities associated with higher absolute voltages and currents per unit area along the antenna. These types of antennas tend to be susceptible to near field coupling which can result in detuning and reduced far field radiation. Additional circuitry and battery power is often needed to compensate for these losses.

Two alternatives to the wire antenna are the patch antenna and the dispersive surface antenna. FIG. 1 is a front view of a prior art patch antenna structure 100. Antenna structure 100 consists of a radiating element 101 etched on one major surface 102 of a substrate 103. On an opposing substrate surface lies an etched ground plane (not shown). The antenna structure 100 includes an antenna feed 104 for feeding a radio frequency (RF) signal to and from the radiating element 101. Both the radiating element 101 and ground plane are typically made of a low loss conducting material such as copper. Substrate 103 may be made of various materials, such as printed circuit board materials. A disadvantage to the patch antenna is that high field concentrations exist between the radiating element 101 and ground plane. These regions absorb power, which ultimately gets converted to heat loss. Furthermore, most patch antennas have very narrow bandwidths, and those having wider bandwidths generally suffer from higher levels of loss and lower antenna radiation performance. While patch antennas can usually provide a good mechanical fit into most of today's communications devices, they are not, unfortunately, capable of meeting many of the required electrical standards.

FIG. 2 shows a prior art dispersive surface antenna structure 200. Antenna 200 includes a radiating element 201 etched onto one side of a substrate 202 which is located in a plane perpendicular to a ground surface 203, such as a radio case or equivalent. The mounting of antenna structure 200 is similar to that of a common monopole antenna. An RF feed 204 provides an input/output path for current. However, currently available dispersive surface antennas are still unable to provide the flexibility to control the frequency domain characteristics of the antenna.

Accordingly, there is a need for an improved dispersive surface antenna structure that overcomes the problems associated with currently available dispersive surface antennas. An antenna structure providing low surface current density features is highly desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a prior art patch antenna structure.

FIG. 2 is a front view of a prior art dispersive surface antenna.

FIG. 3 is an isometric view of an antenna structure formed in accordance with a preferred embodiment of the invention.

FIG. 4 is a front view of the antenna structure of FIG. 3 formed in accordance with the preferred embodiment of the invention.

FIG. 5 is a back view of the antenna structure of FIG. 3 formed in accordance with the preferred embodiment of the invention.

FIG. 6 is a cross-sectional side view of the antenna structure of FIG. 3 formed in accordance with the preferred embodiment of the invention.

FIG. 7 is an antenna structure formed in accordance with an alternative embodiment of the invention.

FIGS. 8-9 are examples of alternative back views for the antenna structures of FIGS. 3 and 7.

FIG. 10 is a communication device employing an antenna structure formed in accordance with the preferred embodiment of the invention.

FIG. 11 is another communication device employing an antenna structure formed in accordance with the preferred embodiment of the invention.

FIG. 12 is an isometric view of an antenna structure formed in accordance with another alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Dispersive surface radiators typically measure near a quarter of free space wavelength along the direction parallel to current flow. These surface radiators work best when located away from grounds or other metallic objects located in parallel planes. In this respect, many dispersive surface antennas behave like quarter wavelength monopole antennas with omni-directional radiation in the plane perpendicular to the current flow direction. A radio case or other form of ground serves the purpose of forming the other half of the antenna system.

Referring now to FIGS. 3, 4, 5, and 6, there are shown isometric, front, back, and cross sectional side views respectively of an antenna 300 formed in accordance with a preferred embodiment of the invention. In accordance with the invention, antenna structure 300 includes a front conductive surface 301, conductive ground posts 302, RF feed 303, conductive ground base 304, and first and second conductive back surfaces 305, 306 having a gap 307 formed therebetween. The conductive surfaces 301, 305, 306 are preferably formed about a planar substrate 309. The substrate 309 and its conductive surfaces 301, 305, 306 are situated perpendicular to the ground base 304.

Front conductive surface 301 is preferably coupled to the first and second conductive back surfaces 305, 306 through vias 312 (shown in FIG. 6) located along side surfaces 308 of substrate 309. Alternatively, a single piece of molded metal can be formed about the substrate in a wrap-around style producing a solid conductive edge along sides 308.

In accordance with the invention, the ground posts 302 are coupled to the ground base 304 and are capacitively coupled to the conductive surfaces of the antenna structure. In accordance with a preferred embodiment of the invention, at least one slot 310 is formed within the front conductive surface 301 to accommodate at least one ground post 302. In accordance with the preferred embodiment of the invention, the ground posts 302 provide both electrical ground and structural support for the antenna structure 300. The grounding posts 302 can be stationary or adjustable. Adjustable ground posts vary the bandwidth of antenna structure 300 while variations in the gap size, width, and location alters the locations and widths of multiple bands. In accordance with the invention, the addition of capacitively coupled back surfaces 305, 306 and the addition of at least one ground post 302 provide a dispersive surface antenna with increased capabilities of multi-band control.

FIG. 7 is a dispersive surface antenna 700 formed in accordance with an alternative embodiment of the invention. In accordance with the alternative embodiment, dispersive surface antenna 700 includes a unitarily molded piece of conductive material formed of front surface 701, side surfaces 708, and first and second back surfaces 705, 706 having a gap 707 formed therebetween. In accordance with the alternative embodiment, front surface 701 is physically supported by a source connection 703. Ground posts 702 extend substantially perpendicular from a ground plate 704. The grounding posts extend into the slots 710 so as to capacitively couple the grounding posts to the front conductive surface 701.

The use of ground posts 302, 702 shown and described in both embodiments provides many benefits. The ground posts 302, 702 provide control of the current flow so as to change the antenna frequency spectra. The ground posts may be implemented as stationary posts or made adjustable by using self-supporting cylindrical sliding rods.

The gaps 307, 707 separating the two back surfaces of the antenna structures 300, 700 can vary in shape, size, and location. By shifting the gap to the side 308, 708, two parallel conductive surfaces become capacitively coupled across the gap, with at least one ground post capacitively coupled to one of the at least two parallel conductive surfaces. The location and shape of the gap can be varied to adjust the antenna frequency spectrum over which the antenna operates. Widening the width of an off-center gap between first and second back surfaces alters the antenna frequency characteristics from multiple bands towards a single, wideband. Widening the width of a centered gap between back surfaces broadens the antenna frequency bandwidth. FIG. 8 shows an example of a slanted gap 802 that has the effect of modifying the multiband characteristics as well as additional flexibility of control. Moving the gap off center tends to split the single bandwidth performance into multiple bands. FIG. 9 shows an example of a straight edge gap 902 being moved off center to vary the frequency response.

Antenna structures 300, 700 have frequency response characteristics adjustable between multiple bands and ultra-wide bands. The antennas 300, 700 of the present invention are self-supporting and can be readily incorporated into many of today's communications products. The capacitive coupling used in both embodiments varies with frequency and thus provides additional freedom to adjust antenna bandwidth and improve return loss.

The antenna structures 300, 700 of the present invention function similarly to quarter wavelength monopole antennas. The addition of the back conductive surfaces 305, 306 and 705, 706 essentially creates a single large wrap-around surface, which effectively spreads out the current flow. Unlike conventional wire antennas (monopoles, dipoles, helices, or loops), the dispersive surface antenna structures 300, 700 of the present invention do not restrict the current flow on the antenna to follow a specific path. As a result, increased bandwidth is obtained by adjusting the ground posts. Furthermore, for any given frequency, the current density on the antenna structures 300, 700 are much lower than typical wire antennas under the same operating conditions, and thus near field losses are minimized, with resulting desired improvements in far field radiation. The dispersive surface antennas 300, 700 have gain characteristics that compare favorably to a monopole wire antenna gain.

The dispersive surface antennas 300, 400 of the present invention are an attractive solution to many of today's communication applications. Two potential applications are shown in FIGS. 10 and 11. FIG. 10 is a communication device 1000, such as a cellular phone, utilizing the antenna structure 300 formed in accordance with the preferred embodiment invention. FIG. 11 shows the antenna structure 300 incorporated into a laptop communicator 1100. The ground posts 302 are shown coupled to the edge of device's ground, such as to the keyboard 1103. The conductive surfaces sit substantially perpendicular to the ground.

FIG. 12 is an isometric view of a dipole antenna structure 1200 formed by the combination of two antenna structures formed in accordance with the preferred embodiment. Here, a dual-coaxial balun 1201 is used to feed two antenna structures 1202, 1204. The first dispersive surface antenna 1202, includes a front conductive surface 1203, at least one grounding post 1205 capacitively coupled to the front conductive surface, and first and second conductive back surfaces 1206, 1209 separated by a gap 1207.

The second dispersive surface antenna 1204 includes a second front conductive surface 1208, a conductive post 1210 capacitively coupled to the second front conductive surface 1208, and third and fourth conductive back surfaces separated by a gap (not shown). The balun 1201 includes first and second shielded portions 1214, 1216, the first shielded portion 1214 carries a radio frequency (RF) signal to the front conducting surface of the first antenna 1202. The first shielded portion 1214 is also coupled to the conductive post 1210 of the second dispersive surface antenna 1204. The second shielded portion 1216 is coupled to the second front conductive surface 1208 of the second dispersive antenna 1204. Ground posts 1205 connect to the second shielded portion 1216 of a balun 1201, such as a Roberts balun known in the art. The antenna assembly 1200 provides a 180-degree phase shift between the first and second dispersive surface antennas 1202, 1204. This antenna structure provides the advantages of broadband or multiband performance along with low surface current densities.

The dispersive antenna structures of the present invention provide low surface current density performance. This type of performance provides the benefits of improved antenna efficiency and reduced battery power consumption. The benefits of wider bandwidth, improved return loss and gain, improved selectivity, and multiband capability, that are generally heavily compromised in prior art antennas, are all advantages achieved with the dispersive surface antenna(s) of the present invention. The use of grounding posts, conductive surface areas, gaps, and symmetrical/asymmetrical alterations make the antenna structure of the present invention quite versatile. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4980694 *Apr 14, 1989Dec 25, 1990Goldstar Products Company, LimitedPortable communication apparatus with folded-slot edge-congruent antenna
US5410749 *Dec 9, 1992Apr 25, 1995Motorola, Inc.Radio communication device having a microstrip antenna with integral receiver systems
US6008773 *May 18, 1998Dec 28, 1999Nihon Dengyo Kosaku Co., Ltd.Reflector-provided dipole antenna
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6369771 *Jan 31, 2001Apr 9, 2002Tantivy Communications, Inc.Low profile dipole antenna for use in wireless communications systems
US6419506 *Jan 20, 2000Jul 16, 20023Com CorporationCombination miniature cable connector and antenna
US6445348 *May 26, 2000Sep 3, 2002Motorola, Inc.Dispersive surface antenna
US6567056 *Nov 13, 2001May 20, 2003Intel CorporationHigh isolation low loss printed balun feed for a cross dipole structure
US7009566Jul 25, 2002Mar 7, 2006Kathrein-Werke AgAntenna for DVB-T reception
US7042403 *Jan 23, 2004May 9, 2006General Motors CorporationDual band, low profile omnidirectional antenna
US7605769 *Apr 16, 2007Oct 20, 2009Samsung Electro-Mechanics Co., Ltd.Multi-ban U-slot antenna
US8228254 *Jun 14, 2001Jul 24, 2012Heinrich FoltzMiniaturized antenna element and array
EP1257001A1 *May 12, 2001Nov 13, 2002TELEFONAKTIEBOLAGET LM ERICSSON (publ)Interface between a mobile radio device and its accessory device based on capacitive coupling for sharing ground planes to rise antenna gain of accessory device
Classifications
U.S. Classification343/702, 343/846, 343/830
International ClassificationH01Q9/30, H01Q9/32, H01Q1/24, H01Q9/42
Cooperative ClassificationH01Q9/32, H01Q9/42, H01Q9/30, H01Q1/241, H01Q1/242
European ClassificationH01Q9/32, H01Q9/30, H01Q1/24A1, H01Q9/42, H01Q1/24A
Legal Events
DateCodeEventDescription
Jan 29, 2013FPExpired due to failure to pay maintenance fee
Effective date: 20121212
Dec 12, 2012LAPSLapse for failure to pay maintenance fees
Jul 23, 2012REMIMaintenance fee reminder mailed
Apr 6, 2011ASAssignment
Owner name: MOTOROLA SOLUTIONS, INC., ILLINOIS
Free format text: CHANGE OF NAME;ASSIGNOR:MOTOROLA, INC;REEL/FRAME:026081/0001
Effective date: 20110104
May 15, 2008FPAYFee payment
Year of fee payment: 8
May 28, 2004FPAYFee payment
Year of fee payment: 4
Jun 1, 1999ASAssignment
Owner name: MOTOROLA, INC., ILLINOIS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MCCOY, DANNY O.;NIU, FENG;REEL/FRAME:010005/0953
Effective date: 19990526